This application is based on Application No. 2001-012205, filed in Japan on Jan. 19, 2001, the contents of which are hereby incorporated by reference to the extent permitted by United States patent law.
1. Field of the Invention
The present invention relates to an automotive alternator and particularly to an automotive alternator in which an electrically-insulating resin is applied to a coil end group of a stator winding to reduce electromagnetic noise caused by vibration of a stator core.
2. Description of the Related Art
Generally, in an automotive alternator, electromagnetic noise is generated by a stator core vibrating in a radial direction during power generation. Thus, conventionally, in order to reduce the electromagnetic noise caused by the vibration of the stator core, countermeasures have been taken to increase rigidity of a stator as a whole by impregnating a varnish into slots to fix the stator core and a stator winding together. According to this countermeasure, because the stator winding is prevented from moving within the slots, damage to an electrically-insulating coating on conductor wires constituting the stator winding resulting from the conductor wires rubbing against an inner wall surface of the slots is suppressed, and withstand voltage between the stator core and the stator winding increases, that is, electrical insulation is also improved.
However, there have been cases where the varnish adhered slightly to coil end groups of the stator winding when impregnating the varnish into the slots, but no thought was given to increasing rigidity of the stator as a whole by actively applying the varnish to the coil end groups. Furthermore, in this countermeasure, because the conductor wires constituting the coil end groups are not fixed to each other, the conductor wires rub against each other due to the vibration, damaging the electrically-insulating coating on the conductor wires, and inducing short-circuiting accidents within and between winding phase portions. In addition, in this countermeasure, narrow gaps are formed between the conductor wires constituting the coil end groups, and because a cooling airflow generated by a cooling fan flows through the narrow gaps, a loud wind noise is generated.
Conventionally, in order to ensure electrical insulation in the coil end groups of the stator winding, countermeasures have been applied to embed the coil end groups entirely in an electrically-insulating resin such as an epoxy resin, etc. In that case, the conductor wires constituting the coil end groups are fixed by the electrically-insulating resin, leading to improved rigidity of the stator as a whole, and gaps between the conductor wires constituting the coil end groups are embedded in the electrically-insulating resin, leading to wind noise reduction.
However, because the coil end groups are embedded entirely in the electrically-insulating resin, heat generated in the stator winding is less likely to dissipate and the stator temperature rises, resulting in decreased output.
Thus, in the conventional automotive alternator, when applying the electrically-insulating resin to the coil end groups of the stator winding, consideration has not been given to both improving rigidity of the stator as a whole and improving cooling of the stator winding. Thus, one problem that has arisen has been that when electromagnetic noise can be reduced, temperature increases in the stator cannot be suppressed. Another problem that has arisen has been that when temperature increases in the stator can be suppressed, electromagnetic noise cannot be reduced.
The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator enabling electromagnetic noise to be reduced while also ensuring cooling of a stator by regulating a space factor of an electrically-insulating resin and conductor wires constituting crossover portions of a coil end group of a stator winding relative to a cross-sectional area of the crossover portions from the viewpoint of electromagnetic noise, and regulating a ratio occupied by exposed portions of conductor wires relative to an outer circumference of the cross section of the crossover portion from the viewpoint of cooling of the stator winding.
In order to achieve the above object, according to one aspect of the present invention, there is provided an automotive alternator including:
a shaft rotatably supported in a case;
a rotor fixed to the shaft;
a stator provided with:
a cylindrical stator core supported in the case so as to envelop the rotor, a plurality of slots extending axially being formed in the stator core so as to line up circumferentially; and
a stator winding composed of a polyphase alternating-current winding installed in the stator core; and
a cooling fan fixed to at least one axial end portion of the rotor,
the polyphase alternating-current winding being constituted by winding phase portions each being constructed by winding a conductor wire for a predetermined number of turns into a wave shape in the slots at intervals of a predetermined number of slots so as to extend outwards from first slots at an end surface of the stator core, extend in a circumferential direction, and enter second slots the predetermined number of slots away, the conductor wire being formed by coating an electrical conductor with electrical insulation, slots in which each of the winding phase portions is installed being offset by one slot from slots in which other of the winding phase portions are installed,
coil ends of the winding phase portions each being constituted by extended portions composed of portions of the conductor wire extending outwards at an end surface of the stator core from a pair of the slots the predetermined number of slots apart, and a crossover portion composed of a portion of the conductor wire extending in a circumferential direction and linking the extended portions extending outwards at the end surface of the stator core from the pair of the slots the predetermined number of slots apart,
a coil end group of the stator winding being constructed by arranging the coil ends of the winding phase portions circumferentially such that the crossover portions overlap radially, and
an electrically-insulating resin being applied to the crossover portions so as to fix together the radially-overlapping crossover portions,
wherein a space factor of the conductor wires and the electrically-insulating resin relative to a cross-sectional area of the crossover portions in a cross section of the crossover portions relative to a plane including an axial center of the stator core is seventy percent (70%) or more, and
a ratio occupied by exposed portions of the conductor wires relative to an outer circumference of the crossover portions in the cross section of the crossover portions is fifty percent (50%) or more.
The electrically-insulating resin may be impregnated inside the slots.
The electrically-insulating resin may be a varnish.
The electrically-insulating resin may be a silicone resin.
The slots may be formed at a ratio of two per phase per pole, the polyphase alternating-current winding being constituted by two three-phase alternating-current windings each formed by connecting three of the winding phase portions into an alternating-current connection.
Each of the winding phase portions may be formed into a divided winding portion.